Many commercial enclosed spaces need to be equipped with pressure relief ports which are sometimes referred to as ventilator ports. This is particularly true where the sealed space is subjected to temperature related gas volume variations that must be relieved.
Many of these enclosed spaces require that a positive air pressure differential to ambience be maintained. For example, clean rooms often require this as do paint spray booths to prevent entry of ambient dust. As exemplified in U.S. Pat. No. 5,820,456, they typically maintain a positive differential by control of intake and exhaust fan speeds. However there are spaces where no differential is required or desired. Passive ports are suitable for these. However existing passive pressure relief ports, meaning those without fans or blowers, have often permitted air migration where there is no significant pressure differential. With walk-in freezers this causes undesirable condensation and frosting. Frosting is a substantial problem that occurs as ambient warm air drawn into a low temperature chamber releases significant amounts of moisture relative to the change in dew point of the air at high and low temperatures. Air is drawn through the port after each door opening cycle as the warm air that entered cools and contracts. If venting does not occur, a partial vacuum results which make it difficult to reopen the door. In extreme cases, the enclosures can even collapse.
A temperature rise in the enclosure between cooling cycles, and especially during a defrost cycle, creates a need to vent air to prevent pressure buildup. Again, failure to vent this pressure, with adequate relief capacity, can cause the chamber to rupture.
Passive pressure relief ports are in wide commercial use today. However, they have a number of limitations and disadvantages. Many have in line valves located within housings that extend through walls. Their space requirements dictate that they be larger than the wall thickness and thus protrude from one or both sides of the wall. Where they extend into a freezer, it is difficult to prevent ice from forming, even with internal heaters. Their valves are often spring loaded and thus over time lose sensitivity. This results in leaky valves that permit air and moisture migration and seepage, which can cause frosting and icing.
Accordingly, it is seen that a need exists for a passive pressure relief port, i.e. one that is not electrically powered by fans and baffles, which can relieve both positive and negative pressure differentials, yet which substantially prevents air migration under static differential conditions. A need also exists for such a pressure relief port which has high flow capacity and yet which is of such small and economic construction that it can be readily mounted in a door jamb or wall. Again, being mountable in a door jamb is desirable so that it may have a heater, to prevent internal ice formation, that can be easily wired to a light switch box that normally is located near door jambs. It thus is to be provision of such a pressure relief port that the present invention is primarily directed.